1. Field of the Invention
This invention relates to the production of gasexpanded polymeric materials with a new class of chemical blowing agents, namely certain hydrazodicarboxylates. These compounds are novel.
2. Description of the Prior Art
Blowing agents which decompose at relatively high temperatures are not new. U.S. Pat. No. 3,235,519 discloses using sulfonyl semicarbazides as blowing agents for polymeric materials which soften above 170.degree.C. These blowing agents are particularly suitable for expanding high density polyethylenes, and many other rubbery and plastic polymers.
U.S. Pat. NO. 3,554,397 discloses the use of certain dihydrocarbyl, especially dimethyl and diethyl, hdyrazodicarboxylates, as blowing agents in polyamide type polymers. However, this patent does not suggest the particular hydrazodicarboxylates of the present invention or the unexpected advantages thereof which are discussed below.